Method and apparatus to control motor cooling in an electro-mechanical transmission

ABSTRACT

A method for controlling a powertrain including an transmission coupled to an engine and an electric machine and a hydraulic control system providing hydraulic flow to a cooling circuit of the electric machine, wherein the transmission is adapted to selectively transmit mechanical power to an output membe, includes monitoring a temperature of the electric machine, determining a cooling flow requirement for the cooling circuit based upon the temperature of the electric machine, comparing the cooling flow requirement to a threshold cooling flow, and requesting active electric machine cooling of the electric machine based upon the comparing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/982,865 filed on Ser. No. 10/26/2007 which is hereby incorporatedherein by reference.

TECHNICAL FIELD

This disclosure pertains to control systems for electro-mechanicaltransmissions.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Known powertrain architectures include torque-generative devices,including internal combustion engines and electric machines, whichtransmit torque through a transmission device to an output member. Oneexemplary powertrain includes a two-mode, compound-split,electro-mechanical transmission which utilizes an input member forreceiving motive torque from a prime mover power source, preferably aninternal combustion engine, and an output member. The output member canbe operatively connected to a driveline for a motor vehicle fortransmitting tractive torque thereto. Electric machines, operative asmotors or generators, generate a torque input to the transmission,independently of a torque input from the internal combustion engine. Theelectric machines may transform vehicle kinetic energy, transmittedthrough the vehicle driveline, to electrical energy that is storable inan electrical energy storage device. A control system monitors variousinputs from the vehicle and the operator and provides operationalcontrol of the powertrain, including controlling transmission operatingstate and gear shifting, controlling the torque-generative devices, andregulating the electrical power interchange among the electrical energystorage device and the electric machines to manage outputs of thetransmission, including torque and rotational speed. A hydraulic controlsystem is known to provide pressurized hydraulic fluid for a number offunctions throughout the powertrain.

Operation of the above devices within a hybrid powertrain vehiclerequire management of numerous torque bearing shafts or devicesrepresenting connections to the above mentioned engine, electricalmachines, and driveline. Input torque from the engine and input torquefrom the electric machine or electric machines can be appliedindividually or cooperatively to provide output torque. Various controlschemes and operational connections between the various aforementionedcomponents of the hybrid drive system are known, and the control systemmust be able to engage to and disengage the various components from thetransmission in order to perform the functions of the hybrid powertrainsystem. Engagement and disengagement are known to be accomplished withinthe transmission by employing selectively operable clutches.

Clutches are devices well known in the art for engaging and disengagingshafts including the management of rotational velocity and torquedifferences between the shafts. Clutches are known in a variety ofdesigns and control methods. One known type of clutch is a mechanicalclutch operating by separating or joining two connective surfaces, forinstance, clutch plates, operating, when joined, to apply frictionaltorque to each other. One control method for operating such a mechanicalclutch includes applying the hydraulic control system implementingfluidic pressures transmitted through hydraulic lines to exert orrelease clamping force between the two connective surfaces. Operatedthusly, the clutch is not operated in a binary manner, but rather iscapable of a range of engagement states, from fully disengaged, tosynchronized but not engaged, to engaged but with only minimal clampingforce, to engaged with some maximum clamping force. The clamping forceavailable to be applied to the clutch determines how much reactivetorque the clutch can carry before the clutch slips.

The hydraulic control system, as described above, utilizes lines filledwith hydraulic fluid to selectively activate clutches within thetransmission. However, the hydraulic control system can also perform anumber of other functions in a hybrid powertrain. For example, anelectric machine utilized within a hybrid powertrain generates heat.Hydraulic fluid from the hydraulic control system can be utilized in anelectric machine cooling circuit to provide an electric machine coolingflow based upon or proportional to hydraulic line pressure (P_(LINE)).Additionally, hydraulic fluid from the hydraulic control system can beutilized to lubricate mechanical devices, such as bearings. Also,hydraulic circuits are known to include some level of internal leakage.

Hydraulic fluid is known to be pressurized within a hydraulic controlsystem with a pump. The pump can be electrically powered or preferablymechanically driven. In addition to this first main hydraulic pump,hydraulic control systems are known to also include an auxiliaryhydraulic pump. The internal impelling mechanism operates at some speed,drawing hydraulic fluid from a return line and pressurizing thehydraulic control system. The supply of hydraulic flow by the pump orpumps is affected by the speed of the pumps, the back pressure exertedby P_(LINE), and the temperature of the hydraulic fluid (T_(OIL)).

The resulting or net P_(LINE) within the hydraulic control system isimpacted by a number of factors. FIG. 1 schematically illustrates amodel of factors impacting hydraulic flow in an exemplary hydrauliccontrol system, in accordance with the present disclosure. As one havingordinary skill in the art will appreciate, conservation of mass explainsthat, in steady state, flow entering a system must equal the flowexiting from that system. As applied to FIG. 1, a flow of hydraulic oilis supplied to the hydraulic control system by the pumps. The flow exitsthe hydraulic control system through the various functions served by thehydraulic control system. P_(LINE) describes the resulting charge ofhydraulic oil maintained in the system. Changes to flows out of thehydraulic control system affect P_(LINE). For any flow through a system,the resulting pressure within the system depends upon the flowresistance within the system. Higher flow resistance, for instanceindicating lower flow usage by the functions served by the hydrauliccontrol system, results in higher P_(LINE) for a given flow. Conversely,lower flow resistance, doe instance indicating higher flow usage by thefunctions served by the hydraulic control system, results in lowersystem pressures for a given flow. Applied to FIG. 1, P_(LINE) changesdepending upon usage of the hydraulic control system. For example,filling a previously unfilled transmission clutch consumes a significantamount of hydraulic oil from the hydraulic control system. The orificeleading to the clutch includes low resistance in order to draw thesignificant amount of hydraulic oil over a short time span. As a result,during the clutch filling process, P_(LINE) in an otherwise unchangedhydraulic control system will reduce. Conversely, for a given set offunctions served by the hydraulic control system, P_(LINE) varies basedupon the flow supplied by the pumps. An increase in flow supplied by apump will increase P_(LINE) in an otherwise unchanged hydraulic controlsystem. For any given set of flow restrictions associated with thefunctions served, increased flow from the pumps will result in higherP_(LINE).

The electric machine cooling function served by the hydraulic controlsystem includes some flow of hydraulic oil to the electric machine ormachines utilized by the hybrid powertrain. As is well known in the art,heat generated by an electric machine increases as the rotational speedof the electric machine. However, as described above, the rate ofhydraulic oil and, therefore, the cooling capacity of the hydraulic oilflowing through an electric machine cooling loop increase only withP_(LINE). As a result, situations can occur where high electric machineusage and low P_(LINE) result in the electric machine not receivingsufficient cooling. Such a condition can be avoided by designing theflow restriction of the coolant loop to provide sufficient cooling forall foreseeable operating conditions of the electric machine, but such adesign requires an excessive flow of hydraulic oil during periods whenthe cooling requirements of the electric machine do not warrant the highflow. A method to control electric machine cooling flow in a hydrauliccontrol system based upon electric machine temperature would bebeneficial.

SUMMARY

A method for controlling a powertrain including an electro-mechanicaltransmission mechanically-operatively coupled to an internal combustionengine and an electric machine and a hydraulic control system providinghydraulic flow to a cooling circuit of the electric machine, wherein thetransmission is adapted to selectively transmit mechanical power to anoutput member, includes monitoring a temperature of the electricmachine, determining a cooling flow requirement for the cooling circuitbased upon the temperature of the electric machine, comparing thecooling flow requirement to a threshold cooling flow, and requestingactive electric machine cooling of the electric machine based upon thecomparing.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 schematically illustrates a model of factors impacting hydraulicflow in an exemplary hydraulic control system, in accordance with thepresent disclosure;

FIG. 2 is a schematic diagram of an exemplary powertrain, in accordancewith the present disclosure;

FIG. 3 is a schematic diagram of an exemplary architecture for a controlsystem and powertrain, in accordance with the present disclosure;

FIG. 4 is a schematic diagram of a hydraulic circuit, in accordance withthe present disclosure;

FIG. 5 schematically illustrates an exemplary information flow forcontrolling an active electric machine cooling circuit, in accordancewith the present disclosure; and

FIG. 6 schematically illustrates an electric machine cooling circuit,wherein a base electric machine cooling flow and an active electricmachine cooling flow are added to form a total electric machine coolingflow, in accordance with the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purposeof illustrating certain exemplary embodiments only and not for thepurpose of limiting the same, FIGS. 2 and 3 depicts an exemplaryelectro-mechanical hybrid powertrain, in accordance with the presentdisclosure. The exemplary electromechanical hybrid powertrain inaccordance with the present disclosure is depicted in FIG. 2, comprisinga two-mode, compound-split, electromechanical hybrid transmission 10operatively connected to an engine 14 and first and second electricmachines (‘MG-A’) 56 and (‘MG-B’) 72. The engine 14 and first and secondelectric machines 56 and 72 each generate power which can be transmittedto the transmission 10. The power generated by the engine 14 and thefirst and second electric machines 56 and 72 and transmitted to thetransmission 10 is described in terms of input torques, referred toherein as T₁, T_(A), and T_(B) respectively, and speed, referred toherein as N_(I), N_(A), and N_(B), respectively.

The exemplary engine 14 comprises a multi-cylinder internal combustionengine selectively operative in several states to transmit torque to thetransmission 10 via an input shaft 12, and can be either aspark-ignition or a compression-ignition engine. The engine 14 includesa crankshaft (not shown) operatively coupled to the input shaft 12 ofthe transmission 10. A rotational speed sensor 11 monitors rotationalspeed of the input shaft 12. Power output from the engine 14, comprisingrotational speed and output torque, can differ from the input speed,N_(I), and the input torque, T₁, to the transmission 10 due to placementof torque-consuming components on the input shaft 12 between the engine14 and the transmission 10,, e.g., a hydraulic pump (not shown) and/or atorque management device (not shown).

The exemplary transmission 10 comprises three planetary-gear sets 24, 26and 28, and four selectively engageable torque-transmitting devices,i.e., clutches C1 70, C2 62, C3 73, and C4 75. As used herein, clutchesrefer to any type of friction torque transfer device including single orcompound plate clutches or packs, band clutches, and brakes, forexample. A hydraulic control circuit 42, preferably controlled by atransmission control module (hereafter ‘TCM’) 17, is operative tocontrol clutch states. Clutches C2 62 and C4 75 preferably comprisehydraulically-applied rotating friction clutches. Clutches C1 70 and C373 preferably comprise hydraulically-controlled stationary devices thatcan be selectively grounded to a transmission case 68. Each of theclutches C1 70, C2 62, C3 73, and C4 75 is preferably hydraulicallyapplied, selectively receiving pressurized hydraulic fluid via thehydraulic control circuit 42.

The first and second electric machines 56 and 72 preferably comprisethree-phase AC machines, each including a stator (not shown) and a rotor(not shown), and respective resolvers 80 and 82. The motor stator foreach machine is grounded to an outer portion of the transmission case68, and includes a stator core with coiled electrical windings extendingtherefrom. The rotor for the first electric machine 56 is supported on ahub plate gear that is operatively attached to shaft 60 via the secondplanetary gear set 26. The rotor for the second electric machine 72 isfixedly attached to a sleeve shaft hub 66.

Each of the resolvers 80 and 82 preferably comprises a variablereluctance device including a resolver stator (not shown) and a resolverrotor (not shown). The resolvers 80 and 82 are appropriately positionedand assembled on respective ones of the first and second electricmachines 56 and 72. Stators of respective ones of the resolvers 80 and82 are operatively connected to one of the stators for the first andsecond electric machines 56 and 72. The resolver rotors are operativelyconnected to the rotor for the corresponding first and second electricmachines 56 and 72. Each of the resolvers 80 and 82 is signally andoperatively connected to a transmission power inverter control module(hereafter ‘TPIM’) 19, and each senses and monitors rotational positionof the resolver rotor relative to the resolver stator, thus monitoringrotational position of respective ones of first and second electricmachines 56 and 72. Additionally, the signals output from the resolvers80 and 82 are interpreted to provide the rotational speeds for first andsecond electric machines 56 and 72, i.e., N_(A) and N_(B), respectively.

The transmission 10 includes an output member 64, e.g. a shaft, which isoperably connected to a driveline 90 for a vehicle (not shown), toprovide output power, e.g., to vehicle wheels 93, one of which is shownin FIG. 2. The output power is characterized in terms of an outputrotational speed, N_(O) and an output torque, T_(O). A transmissionoutput speed sensor 84 monitors rotational speed and rotationaldirection of the output member 64. Each of the vehicle wheels 93, ispreferably equipped with a sensor 94 adapted to monitor wheel speed,V_(SS-WHL), the output of which is monitored by a control module of adistributed control module system described with respect to FIG. 3, todetermine vehicle speed, and absolute and relative wheel speeds forbraking control, traction control, and vehicle acceleration management.

The input torques from the engine 14 and the first and second electricmachines 56 and 72 (T₁, T_(A), and T_(B) respectively) are generated asa result of energy conversion from fuel or electrical potential storedin an electrical energy storage device (hereafter ‘ESD’) 74. The ESD 74is high voltage DC-coupled to the TPIM 19 via DC transfer conductors 27.The transfer conductors 27 include a contactor switch 38. When thecontactor switch 38 is closed, under normal operation, electric currentcan flow between the ESD 74 and the TPIM 19. When the contactor switch38 is opened electric current flow between the ESD 74 and the TPIM 19 isinterrupted. The TPIM 19 transmits electrical power to and from thefirst electric machine 56 by transfer conductors 29, and the TPIM 19similarly transmits electrical power to and from the second electricmachine 72 by transfer conductors 31, in response to torque commands forthe first and second electric machines 56 and 72 to achieve the inputtorques T_(A) and T_(B). Electrical current is transmitted to and fromthe ESD 74 in accordance with whether the ESD 74 is being charged ordischarged.

The TPIM 19 includes the pair of power inverters (not shown) andrespective motor control modules (not shown) configured to receive thetorque commands and control inverter states therefrom for providingmotor drive or regeneration functionality to meet the commanded motortorques T_(A) and T_(B). The power inverters comprise knowncomplementary three-phase power electronics devices, and each includes aplurality of insulated gate bipolar transistors (not shown) forconverting DC power from the ESD 74 to AC power for powering respectiveones of the first and second electric machines 56 and 72, by switchingat high frequencies. The insulated gate bipolar transistors form aswitch mode power supply configured to receive control commands. Thereis typically one pair of insulated gate bipolar transistors for eachphase of each of the three-phase electric machines. States of theinsulated gate bipolar transistors are controlled to provide motor drivemechanical power generation or electric power regenerationfunctionality. The three-phase inverters receive or supply DC electricpower via DC transfer conductors 27 and transform it to or fromthree-phase AC power, which is conducted to or from the first and secondelectric machines 56 and 72 for operation as motors or generators viatransfer conductors 29 and 31 respectively.

FIG. 3 is a schematic block diagram of the distributed control modulesystem. The elements described hereinafter comprise a subset of anoverall vehicle control architecture, and provide coordinated systemcontrol of the exemplary powertrain described in FIG. 2. The distributedcontrol module system synthesizes pertinent information and inputs, andexecutes algorithms to control various actuators to achieve controlobjectives, including objectives related to fuel economy, emissions,performance, drivability, and protection of hardware, includingbatteries of ESD 74 and the first and second electric machines 56 and72. The distributed control module system includes an engine controlmodule (hereafter ‘ECM’) 23, the TCM 17, a battery pack control module(hereafter ‘BPCM’) 21, and the TPIM 19. A hybrid control module(hereafter ‘HCP’) 5 provides supervisory control and coordination of theECM 23, the TCM 17, the BPCM 21, and the TPIM 19. A user interface(‘UI’) 13 is operatively connected to a plurality of devices throughwhich a vehicle operator controls or directs operation of theelectromechanical hybrid powertrain. The devices include an acceleratorpedal 113 (‘AP’) from which an operator torque request is determined, anoperator brake pedal 112 (‘BP’), a transmission gear selector 114(‘PRNDL’), and a vehicle speed cruise control (not shown). Thetransmission gear selector 114 may have a discrete number ofoperator-selectable positions, including the rotational direction of theoutput member 64 to enable one of a forward and a reverse direction.

The aforementioned control modules communicate with other controlmodules, sensors, and actuators via a local area network (hereafter‘LAN’) bus 6. The LAN bus 6 allows for structured communication ofstates of operating parameters and actuator command signals between thevarious control modules. The specific communication protocol utilized isapplication-specific. The LAN bus 6 and appropriate protocols providefor robust messaging and multi-control module interfacing between theaforementioned control modules, and other control modules providingfunctionality such as antilock braking, traction control, and vehiclestability. Multiple communications buses may be used to improvecommunications speed and provide some level of signal redundancy andintegrity. Communication between individual control modules can also beeffected using a direct link, e.g., a serial peripheral interface(‘SPI’) bus (not shown).

The HCP 5 provides supervisory control of the powertrain, serving tocoordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Basedupon various input signals from the user interface 13 and thepowertrain, including the ESD 74, the HCP 5 generates various commands,including: the operator torque request (‘T_(O) _(—) _(REQ)’), acommanded output torque (‘T_(CMD)’) to the driveline 90, an engine inputtorque command, clutch torques for the torque-transfer clutches C1 70,C2 62, C3 73, C4 75 of the transmission 10; and the torque commands forthe first and second electric machines 56 and 72, respectively. The TCM17 is operatively connected to the hydraulic control circuit 42 andprovides various functions including monitoring various pressure sensingdevices (not shown) and generating and communicating control signals tovarious solenoids (not shown) thereby controlling pressure switches andcontrol valves contained within the hydraulic control circuit 42.

The ECM 23 is operatively connected to the engine 14, and functions toacquire data from sensors and control actuators of the engine 14 over aplurality of discrete lines, shown for simplicity as an aggregatebi-directional interface cable 35. The ECM 23 receives the engine inputtorque command from the HCP 5. The ECM 23 determines the actual engineinput torque, T₁, provided to the transmission 10 at that point in timebased upon monitored engine speed and load, which is communicated to theHCP 5. The ECM 23 monitors input from the rotational speed sensor 11 todetermine the engine input speed to the input shaft 12, which translatesto the transmission input speed, N_(I). The ECM 23 monitors inputs fromsensors (not shown) to determine states of other engine operatingparameters including, e.g., a manifold pressure, engine coolanttemperature, ambient air temperature, and ambient pressure. The engineload can be determined, for example, from the manifold pressure, oralternatively, from monitoring operator input to the accelerator pedal113. The ECM 23 generates and communicates command signals to controlengine actuators, including, e.g., fuel injectors, ignition modules, andthrottle control modules, none of which are shown.

The TCM 17 is operatively connected to the transmission 10 and monitorsinputs from sensors (not shown) to determine states of transmissionoperating parameters. The TCM 17 generates and communicates commandsignals to control the transmission 10, including controlling thehydraulic control circuit 42. Inputs from the TCM 17 to the HCP 5include estimated clutch torques for each of the clutches, i.e., C1 70,C2 62, C3 73, and C4 75, and rotational output speed, N_(O), of theoutput member 64. Other actuators and sensors may be used to provideadditional information from the TCM 17 to the HCP 5 for controlpurposes. The TCM 17 monitors inputs from pressure switches (not shown)and selectively actuates pressure control solenoids (not shown) andshift solenoids (not shown) of the hydraulic control circuit 42 toselectively actuate the various clutches C1 70, C2 62, C3 73, and C4 75to achieve various transmission operating range states, as describedhereinbelow.

The BPCM 21 is signally connected to sensors (not shown) to monitor theESD 74, including states of electrical current and voltage parameters,to provide information indicative of parametric states of the batteriesof the ESD 74 to the HCP 5. The parametric states of the batteriespreferably include battery state-of-charge, battery voltage, batterytemperature, and available battery power, referred to as a range P_(BAT)_(—) _(MIN) to P_(BAT) _(—) _(MAX).

Each of the control modules ECM 23, TCM 17, TPIM 19 and BPCM 21 ispreferably a general-purpose digital computer comprising amicroprocessor or central processing unit, storage mediums comprisingread only memory (‘ROM’), random access memory (‘RAM’), electricallyprogrammable read only memory (‘EPROM’), a high speed clock, analog todigital (‘A/D’) and digital to analog (‘D/A’) circuitry, andinput/output circuitry and devices (‘I/O’) and appropriate signalconditioning and buffer circuitry. Each of the control modules has a setof control algorithms, comprising resident program instructions andcalibrations stored in one of the storage mediums and executed toprovide the respective functions of each computer. Information transferbetween the control modules is preferably accomplished using the LAN bus6 and SPI buses. The control algorithms are executed during preset loopcycles such that each algorithm is executed at least once each loopcycle. Algorithms stored in the non-volatile memory devices are executedby one of the central processing units to monitor inputs from thesensing devices and execute control and diagnostic routines to controloperation of the actuators, using preset calibrations. Loop cycles areexecuted at regular intervals, for example each 3.125, 6.25, 12.5, 25and 100 milliseconds during ongoing operation of the powertrain.Alternatively, algorithms may be executed in response to the occurrenceof an event.

The exemplary powertrain selectively operates in one of severaloperating range states that can be described in terms of an engine statecomprising one of an engine on state (‘ON’) and an engine off state(‘OFF’), and a transmission state comprising a plurality of fixed gearsand continuously variable operating modes, described with reference toTable 1, below.

TABLE 1 Engine Transmission Operating Applied Description State RangeState Clutches MI_Eng_Off OFF EVT Mode I C1 70 MI_Eng_On ON EVT Mode IC1 70 FG1 ON Fixed Gear Ratio 1 C1 70 C4 75 FG2 ON Fixed Gear Ratio 2 C170 C2 62 MII_Eng_Off OFF EVT Mode II C2 62 MII_Eng_On ON EVT Mode II C262 FG3 ON Fixed Gear Ratio 3 C2 62 C4 75 FG4 ON Fixed Gear Ratio 4 C2 62C3 73

Each of the transmission operating range states is described in thetable and indicates which of the specific clutches C1 70, C2 62, C3 73,and C4 75 are applied for each of the operating range states. A firstcontinuously variable mode, i.e., EVT Mode I, or MI, is selected byapplying clutch C1 70 only in order to “ground” the outer gear member ofthe third planetary gear set 28. The engine state can be one of ON(‘MI_Eng_On’) or OFF (‘MI_Eng_Off’). A second continuously variablemode, i.e., EVT Mode II, or MII, is selected by applying clutch C2 62only to connect the shaft 60 to the carrier of the third planetary gearset 28. The engine state can be one of ON (‘MII_Eng_On’) or OFF(‘MII_Eng_Off’). For purposes of this description, when the engine stateis OFF, the engine input speed is equal to zero revolutions per minute(‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gearoperation provides a fixed ratio operation of input-to-output speed ofthe transmission 10, i.e., N_(I)/N_(O), is achieved. A first fixed gearoperation (‘FG1’) is selected by applying clutches C1 70 and C4 75. Asecond fixed gear operation (‘FG2’) is selected by applying clutches C170 and C2 62. A third fixed gear operation (‘FG3’) is selected byapplying clutches C2 62 and C4 75. A fourth fixed gear operation (‘FG4’)is selected by applying clutches C2 62 and C3 73. The fixed ratiooperation of input-to-output speed increases with increased fixed gearoperation due to decreased gear ratios in the planetary gears 24, 26,and 28. The rotational speeds of the first and second electric machines56 and 72, N_(A) and N_(B) respectively, are dependent on internalrotation of the mechanism as defined by the clutching and areproportional to the input speed measured at the input shaft 12.

In response to operator input via the accelerator pedal 113 and brakepedal 112 as captured by the user interface 13, the HCP 5 and one ormore of the other control modules determine the commanded output torque,T_(CMD), intended to meet the operator torque request, T_(O) _(—)_(REQ), to be executed at the output member 64 and transmitted to thedriveline 90. Final vehicle acceleration is affected by other factorsincluding, e.g., road load, road grade, and vehicle mass. The operatingrange state is determined for the transmission 10 based upon a varietyof operating characteristics of the powertrain. This includes theoperator torque request, communicated through the accelerator pedal 113and brake pedal 112 to the user interface 13 as previously described.The operating range state may be predicated on a powertrain torquedemand caused by a command to operate the first and second electricmachines 56 and 72 in an electrical energy generating mode or in atorque generating mode. The operating range state can be determined byan optimization algorithm or routine which determines optimum systemefficiency based upon operator demand for power, battery state ofcharge, and energy efficiencies of the engine 14 and the first andsecond electric machines 56 and 72. The control system manages torqueinputs from the engine 14 and the first and second electric machines 56and 72 based upon an outcome of the executed optimization routine, andsystem efficiencies are optimized thereby, to manage fuel economy andbattery charging. Furthermore, operation can be determined based upon afault in a component or system. The HCP 5 monitors the torque-generativedevices, and determines the power output from the transmission 10required to achieve the desired output torque to meet the operatortorque request. As should be apparent from the description above, theESD 74 and the first and second electric machines 56 and 72 areelectrically-operatively coupled for power flow therebetween.Furthermore, the engine 14, the first and second electric machines 56and 72, and the electromechanical transmission 10 aremechanically-operatively coupled to transmit power therebetween togenerate a power flow to the output member 64.

FIG. 4 depicts a schematic diagram of the hydraulic control circuit 42for controlling flow of hydraulic fluid in the exemplary transmission. Amain hydraulic pump 88 is driven off the input shaft 12 from the engine14, and an auxiliary pump 110 controlled by the TPIM 19 to providepressurized fluid to the hydraulic control circuit 42 through valve 140.The auxiliary pump 110 preferably comprises an electrically-powered pumpof an appropriate size and capacity to provide sufficient flow ofpressurized hydraulic fluid into the hydraulic control circuit 42 whenoperational. The hydraulic control circuit 42 selectively distributeshydraulic pressure to a plurality of devices, including thetorque-transfer clutches C1 70, C2 62, C3 73, and C4 75, active coolingcircuits for the first and second electric machines 56 and 72 (notshown), and a base cooling circuit for cooling and lubricating thetransmission 10 via passages 142, 144 (not depicted in detail). Aspreviously stated, the TCM 17 actuates the various clutches to achieveone of the transmission operating range states through selectiveactuation of hydraulic circuit flow control devices comprising variablepressure control solenoids (‘PCS’) PCS1 108, PCS2 114, PCS3 112, PCS4116 and solenoid-controlled flow management valves, X-valve 119 andY-valve 121. The hydraulic control circuit 42 is fluidly connected topressure switches PS1, PS2, PS3, and PS4 via passages 122, 124, 126, and128, respectively. The pressure control solenoid PCS1 108 has a controlposition of normally high and is operative to modulate the magnitude offluidic pressure in the hydraulic circuit through fluidic interactionwith controllable pressure regulator 107 and spool valve 109. Thecontrollable pressure regulator 107 and spool valve 109 interact withPCS1 108 to control hydraulic pressure in the hydraulic control circuit42 over a range of pressures and may provide additional functionalityfor the hydraulic control circuit 42. Pressure control solenoid PCS3 112has a control position of normally high, and is fluidly connected tospool valve 113 and operative to effect flow therethrough when actuated.Spool valve 113 is fluidly connected to pressure switch PS3 via passage126. Pressure control solenoid PCS2 114 has a control position ofnormally high, and is fluidly connected to spool valve 115 and operativeto effect flow therethrough when actuated. Spool valve 115 is fluidlyconnected to pressure switch PS2 via passage 124. Pressure controlsolenoid PCS4 116 has a control position of normally low, and is fluidlyconnected to spool valve 117 and operative to effect flow therethroughwhen actuated. Spool valve 117 is fluidly connected to pressure switchPS4 via passage 128.

The X-Valve 119 and Y-Valve 121 each comprise flow management valvescontrolled by solenoids 118, 120, respectively, in the exemplary system,and have control states of High (‘1’) and Low (‘0’). The control statesrefer to positions of each valve to which control flow to differentdevices in the hydraulic control circuit 42 and the transmission 10. TheX-valve 119 is operative to direct pressurized fluid to clutches C3 73and C4 75 and cooling systems for stators of the first and secondelectric machines 56 and 72 via fluidic passages 136, 138, 144, 142respectively, depending upon the source of the fluidic input, as isdescribed hereinafter. The Y-valve 121 is operative to directpressurized fluid to clutches C1 70 and C2 62 via fluidic passages 132and 134 respectively, depending upon the source of the fluidic input, asis described hereinafter. The Y-valve 121 is fluidly connected topressure switch PSI via passage 122.

The hydraulic control circuit 42 includes a base cooling circuit forproviding hydraulic fluid to cool the stators of the first and secondelectric machines 56 and 72. The base cooling circuit includes fluidconduits from the valve 140 flowing directly to a flow restrictor whichleads to fluidic passage 144 leading to the base cooling circuit for thestator of the first electric machine 56, and to a flow restrictor whichleads to fluidic passage 142 leading to the base cooling circuit for thestator of the second electric machine 72. Active cooling of stators forthe first and second electric machines 56 and 72 is effected byselective actuation of pressure control solenoids PCS2 114, PCS3 112 andPCS4 116 and solenoid-controlled flow management valves X-valve 119 andY-valve 121, which leads to flow of hydraulic fluid around the selectedstator and permits heat to be transferred therebetween, primarilythrough conduction.

An exemplary logic table to accomplish control of the exemplaryhydraulic control circuit 42 to control operation of the transmission 10in one of the transmission operating range states is provided withreference to Table 2, below.

TABLE 2 X- Y- Transmission Valve Valve Operating Logic Logic PCS1 PCS2PCS3 PCS4 Range No C2 Normal Normal Normal Normal State Latch Latch HighHigh High Low EVT 0 0 Line MG-B C1 MG-A Mode I Modulation Stator StatorCool Cool EVT 0 1 Line C2 MG-B MG-A Mode II Modulation Stator StatorCool Cool Low 1 0 Line C2 C1 C4 Range Modulation High 1 1 Line C2 C3 C4Range Modulation

A Low Range is defined as a transmission operating range statecomprising one of the first continuously variable mode and the first andsecond fixed gear operations. A High Range is defined as a transmissionoperating range state comprising one of the second continuously variablemode and the third and fourth fixed gear operations. Selective controlof the X-valve 119 and the Y-valve 121 and actuation of the solenoidsPCS2 112, PCS3 114, PCS4 116 facilitate flow of hydraulic fluid toactuate clutches C1 70, C2 63, C3 73, and C4 75, and provide cooling forthe stators the first and second electric machines 56 and 72.

In operation, a transmission operating range state, i.e. one of thefixed gear and continuously variable mode operations, is selected forthe exemplary transmission 10 based upon a variety of operatingcharacteristics of the powertrain. This includes the operator torquerequest, typically communicated through inputs to the UI 13 aspreviously described. Additionally, a demand for output torque ispredicated on external conditions, including, e.g., road grade, roadsurface conditions, or wind load. The operating range state may bepredicated on a powertrain torque demand caused by a control modulecommand to operate of the electrical machines in an electrical energygenerating mode or in a torque generating mode. The operating rangestate can be determined by an optimization algorithm or routine operableto determine an optimum system efficiency based upon the operator torquerequest, battery state of charge, and energy efficiencies of the engine14 and the first and second electric machines 56 and 72. The controlsystem manages the input torques from the engine 14 and the first andsecond electric machines 56 and 72 based upon an outcome of the executedoptimization routine, and system optimization occurs to improve fueleconomy and manage battery charging. Furthermore, the operation can bedetermined based upon a fault in a component or system.

As described above, FIG. 1 illustrates flows entering and exiting ahydraulic control system. Hydraulic control system 200 with inflows andoutflows is illustrated. The resulting pressure, P_(LINE), determinesthe capacity of the functions served by the hydraulic control system.For example, clamping force available to a clutch is directly related toP_(LINE) that can be applied. Electric machine cooling is one offunctions served by the hydraulic control system. While it is necessaryto be able to adequately cool the electric machine or machines, asdescribed above, cooling constantly to the maximum cooling requirementof the electric machine constitutes an excessive drain upon thehydraulic control system, requiring either large pumping capacity fromthe main and auxiliary hydraulic pumps or draining P_(LINE) capacityfrom the other functions served by the hydraulic control system. As aresult, it is preferable to control the flow to the electric machinebased upon the cooling requirements of the electric machine. A method isdescribed to control electric machine cooling based upon electricmachine cooling requirements based upon electric machine temperatures.

Electric machines are configured to receive a cooling hydraulic flowthrough a port, channel the hydraulic flow through a set of passagesconfigured to transfer heat from the electric machine to the hydraulicfluid, and then channel the hydraulic fluid out of the heat exchangingarea through an exhaust port to a hydraulic oil return line. Thepassages within the heat exchanging area are known to include featuresto maximize surface area for the hydraulic fluid to contact, throughfins or other structures, so as to maximize the cooling effect that thehydraulic flow can have upon the electric machine.

As described above, electric machine cooling can include an electricmachine cooling flow, providing a basic or base electric machine coolingflow based upon or proportional to P_(LINE). However, such a coolantflow circuit, providing a base flow, can be insufficient to reducetemperatures in all operating circumstances. Hydraulic fluid from thehydraulic control system can be utilized in a selectable active electricmachine cooling flow to provide additional electric machine cooling,when needed. An exemplary active electric machine cooling circuit isdisclosed, wherein a selectable hydraulic flow circuit providing ahydraulic flow to an electric machine is activated and deactivated basedupon electric machine temperatures.

As in FIG. 4 and Table 2, hydraulic flow in the exemplary hydrauliccontrol system described above is accomplished through control of aplurality of flow management valves and a plurality of PCS devices.Referring to Table 2, active electric machine cooling is enabled when anexemplary X-valve is a zero position. When the X-valve is instead in aone position, fixed gear states are enabled, wherein two clutches can beoperated at one time. This exclusive use of the hydraulic controlsystem, allowing either active electric machine cooling or fixed gearstate operation, is descriptive of choices that are required to operatethe function served by the hydraulic control system based upon a limitedflow of hydraulic fluid. One having ordinary skill in the art willappreciate that flows that can be supplied to the hydraulic controlsystem at any given time are not unlimited, and functions served by thehydraulic control system must be prioritized when too many requests aremade simultaneously of the system. Selecting between functions served bydistinct valve settings enables prioritization based upon valvesettings. Additionally, PCS devices can be used to selectively switch onand off active machine cooling circuits, if the exemplary X-valve is inthe zero position. As described in Table 2 above, PCS devices can beutilized to controllably channel hydraulic fluid in different directionsdepending upon X-valve and Y-valve positions. In the context of anactive electric machine cooling circuit, a PCS valve can be described asallowing flow through the active electric machine cooling circuit in aopen position and blocking flow through the circuit in a closedposition. In this way, active electric machine cooling circuits can beselectively activated based upon valve settings. It will be appreciatedthat the two level, X-valve and PCS device configuration is an exemplaryembodiment of how selective activation of an active electric machinecooling circuit can be accomplished. However, a number of embodimentsare envisioned, including individual valves or devices controlling eachindividual function served by the hydraulic control system, and thisdisclosure is not intended to be limited to the particular embodimentsdescribed herein.

Prioritization of different functions served by the hydraulic controlsystem can be based upon impact to powertrain characteristics, such asdrivability. An example of prioritization can be illustrated by aconflict between a fixed gear state and a request for electric machinecooling. If a fixed gear state is desired and in operation, shifting outof the fixed gear to enable an active motor cooling event will cause atleast one clutch to transition and can impact commanded engine output.This effect upon operation of the powertrain, likely perceivable by anoperator, is an adverse impact to drivability. In an alternativereaction, the fixed gear state can be maintained, and operation of theelectric machine can be sustained to some higher temperature threshold,modulated to some reduced output, or deactivated based upon the electricmachine temperature and known risks of the elevated temperature upon theelectric machine. However, effects upon drivability of different actionstaken to protect the electric machine from elevated temperatures neednot affect drivability. In this way, a selection can be made toprioritize fixed gear operation over active electric machine cooling.

Prioritization of valve settings can improved by careful selection ofvalve configurations. Taking for example the exemplary transmissionconfiguration described above, in fixed gear operation wherein operationincludes two engaged clutches, no active motor cooling is possible.However, in such a configuration, one degree of freedom exists, suchthat a change in input speed as dictated by the input speed results in afixed or determinable output speed. Torques provided bytorque-generating devices sum to act upon the input. By contrast, inmode operation wherein a single clutch is engaged, two degrees offreedom exist, wherein output speed can vary for a given input speedbased upon other variable such as electric machine output. In such asingle clutch setting, electric machine output is actively used tomodulate the resulting output speed. In such a setting, electric machineusage is likely to increase, creating a greater draw in current andresulting in higher cooling requirements in the electric machine.Wherein a single clutch is utilized in a dedicated EVT mode, the valvingstrategy discussed above allows for active cooling and can be utilizedto satisfy the higher cooling requirements described.

High temperatures within electrical components or systems can causedamage or degraded performance. Damage from temperature can come in manyforms known in the art and can cause the electrical components to ceasefunctioning. Higher temperatures in an electrical conductor causesincreased electrical resistance and can alter the performance of theconductor in the system. Temperature of the electric machines can bemonitored using sensors known in the art.

FIG. 5 schematically illustrates an exemplary information flow forcontrolling an active electric machine cooling circuit, in accordancewith the present disclosure. Active electric machine cooling controlsystem 250 comprises a first hydraulic powertrain cooling module 260, asecond hydraulic powertrain cooling module 270, and a hydraulic controlcommand module 280. Hydraulic powertrain cooling module 260 monitorsinputs describing temperatures of an exemplary powertrain comprising twoelectric machines. However, it will be appreciated that system 250 canbe utilized with powertrains including any number of electric machinesor additional functions served by active cooling circuits. Hydraulicpowertrain cooling module 260 applies programmed functions modeling heatrejection rates within the electric machine cooling circuits as afunction of flow through the circuits or utilizes look-up tables totranslate the temperatures of the monitored components into cooling flowrequirements for each component, in this exemplary embodiment, coolingrequirements for the two electric machines. Additionally, hydraulicpowertrain cooling module 260 can input and factor base electric machinecooling flow to determine the cooling flow requirements. For example, ifP_(LINE) is towards a high range, more base electric machine coolingflow will result, reducing a need for active electric machine coolingflow. Flow requirements corresponding to electric machine temperaturesmay be developed experimentally, empirically, predictively, throughmodeling or other techniques adequate to accurately predict electricmachine operation. Hydraulic powertrain cooling module 270 monitors thecooling flow requirements of electric machine A and electric machine Band compares the flow requirements to a threshold flow requirement orrequirements. A threshold flow requirement can be a static number basedupon average cooling capabilities of a base electric machine coolingcircuit, or a requirement can be based upon variable inputs, such asP_(LINE) or expected demands upon the electric machines. A singlethreshold can be utilized to activate an active electric machine coolingrequest, for example, if a cooling flow requirement for an a electricmachine exceeds a threshold, then signal an active electric machinecooling request for that electric machine. Different thresholds can beused for different electric machines, based upon the specific operationor configuration of the powertrain. Alternatively, a single thresholdcan be used to say if a cooling flow requirement for either electricmachine exceeds a threshold, then signal an active electric machinecooling request for both electric machines. Alternatively oradditionally, multiple thresholds can be utilized, for example,additionally requesting modulation of electric machine operation if anelectric machine cooling request is ignored or generating degrees ofactive electric machine cooling request based upon the thresholdexceeded. Hydraulic control command module 280 receives an activeelectric machine cooling request as an input. The active electricmachine cooling request is compared with other demands by functionsserved by the hydraulic control system, in this exemplary embodiment,including transmission clutch requirements and lubrication requirements.Additionally, hydraulic control command module 280 can monitor otherfactors affecting operation of the hydraulic control system. Exemplaryfactors include power loss of a hydraulic pump, describing pump outputas an indicator of P_(LINE); an operating state of the engine describingusage of the electric machines, operation of the main hydraulic pump,and expected transmission shifting; and overall powertrain operation.Based upon the comparison and the effects of any monitored inputs, ifthe active electric machine cooling request can be satisfied, thenhydraulic control system valve commands are issued to activate theactive electric machine cooling circuit. If the other demands of thefunctions served by the hydraulic control system outweigh the activeelectric machine cooling request, then the request is ignored. In thisway, temperatures of electric machines can be used to control activationof an active electric machine cooling circuit.

Active electric machine cooling and base electric machine cooling can beadditive or in the alternative. FIG. 6 schematically illustrates anelectric machine cooling circuit, wherein a base electric machinecooling flow and an active electric machine cooling flow are added toform a total electric machine cooling flow, in accordance with thepresent disclosure. Electric machine cooling circuit 300 comprises a lowflow restrictive orifice 310 and a high flow device 320. As describedabove, P_(LINE) is a variable resulting from the flows entering andexiting the hydraulic control system. Low flow restrictive orifice 310provides a path for base electric machine cooling flow to enter thecooling circuit. However, low flow restrictive orifice 310 utilizes aconstricting orifice, such as a relatively small hole, to create a highflow restriction in the portion of the circuit providing base electricmachine cooling flow. As described above, when temperatures in theelectric machines are not high, it is beneficial to restrain the amountof unnecessary flow to the cooling circuit. High flow device 320provides a path for active electric machine cooling flow to enter thecooling circuit. Cooling flow from an activated active electric machinecooling circuit is preferably greater than a flow from a base electricmachine cooling circuit. For example, an active electric machine coolingcircuit can create ten times the flow of a base electric machine coolingcircuit in the same electric machine cooling circuit. High flow device320 can include a high flow restrictive orifice, controlling the amountof flow resulting from the application of P_(LINE). Alternatively, highflow device 320 can be omitted or be unitary with a PCS devicecontrolling activation of the active electric machine cooling circuit,and the active electric machine cooling circuit can be designed tointrinsically include a particular flow restriction. Flows from the baseelectric machine cooling circuit and the active electric machine coolingcircuit are combined to form the total electric machine cooling flow.

It will be appreciated that selective use of active cooling resulting ingreater hydraulic flow to the electric machines can result in a lowerrequired P_(LINE) than simply utilizing base cooling. The use of acircuit permitting greater flow to the electric motors for a givenP_(LINE) can accomplish greater cooling than use of a circuit permittinglesser flow. In order to accomplish required cooling in a systemutilizing only base cooling, the hydraulic pump would have to create agreater P_(LINE) to compensate, thereby requiring a greater power drawto the pump. In this way, active cooling producing greater flow to theelectric machines can result in lower power usage by the hydrauliccontrol system.

Hydraulic flow through electric machine cooling circuits, as well asthrough other functions served by the hydraulic control system, dependsupon P_(LINE). Modulation of flow entering the hydraulic control systemaffects resulting P_(LINE). P_(LINE) can be either directly monitoredthrough pressure sensors, such as pressure transducers well known in theart, or P_(LINE) can be estimated based upon different variables oroperation of various components. One exemplary method to estimateP_(LINE) is a flow-based model based upon the analysis of FIG. 1,wherein flow entering the system is modeled based upon pump parameters,oil temperature, and estimated back pressure upon the pump; and whereinflow exiting the system is modeled based upon known operationalcharacteristics of functions served by the hydraulic control system. Byintegrating the change in flow through the system or dV/dt through someinterval, the resulting state of the hydraulic control system orP_(LINE) can be estimated. Based upon a known or estimated value ofP_(LINE), operation of the hydraulic control system can be monitored,and in the event of a low or declining P_(LINE) value, actions can betaken to boost P_(LINE). In many configurations, operation of a mainhydraulic pump, properly sized for the hydraulic control system, willproduce adequate flow to maintain P_(LINE). Some embodiments areconfigured such that an auxiliary electrically-powered hydraulic pumpcan be used to boost the main hydraulic, if needed. In embodiments wherethe main hydraulic pump is directly driven, and wherein an enginerunning/engine stopped strategy is employed in the powertrain, anauxiliary pump is used to supply hydraulic pressure. In the event thatthe P_(LINE) drops below a threshold level, the auxiliary pump, runningat some speed, can be commanded to run at some elevated speed up to amaximum speed in order to recover P_(LINE). In the alternative, ifP_(LINE) drops and flows into the system cannot be boosted or elevated,functions served by the hydraulic control system can be selectivelyreduced. For example, if active electric machine cooling circuits to twoelectric machines are both activated, and P_(LINE) drops below athreshold, one of the active electric machine cooling circuits can bede-activated momentarily to allow recovery, or the two active electricmachine cooling circuits can be operated in a selectively alternatingscheme to provide partial cooling to both circuits. In this way, ifoperation of the electric machine coolant circuits causes P_(LINE) todrop, remedial actions can be taken to restore P_(LINE).

It is understood that modifications are allowable within the scope ofthe disclosure. The disclosure has been described with specificreference to the preferred embodiments and modifications thereto.Further modifications and alterations may occur to others upon readingand understanding the specification. It is intended to include all suchmodifications and alterations insofar as they come within the scope ofthe disclosure.

1. Method for controlling a powertrain comprising an electro-mechanicaltransmission mechanically-operatively coupled to an internal combustionengine and an electric machine and a hydraulic control system providinghydraulic flow to a cooling circuit of said electric machine, saidtransmission adapted to selectively transmit mechanical power to anoutput member, said method comprising: monitoring a temperature of saidelectric machine; determining a cooling flow requirement for saidcooling circuit based upon said temperature of said electric machine;comparing said cooling flow requirement to a threshold cooling flow; andrequesting active electric machine cooling of said electric machinebased upon said comparing.
 2. The method of claim 1, further comprising:monitoring flow requirements of other functions served by said hydrauliccontrol system; and commanding activation of an active cooling circuitof said electric machine based upon said requesting active electricmotor cooling and said flow requirements of other functions.
 3. Themethod of claim 2, further comprising: monitoring an operating state ofsaid engine; and wherein said commanding activation of said activecooling circuit is further based upon said operating state of saidengine.
 4. The method of claim 2, further comprising: monitoring ahydraulic line pressure of said hydraulic control system; and whereinsaid commanding activation of said active cooling circuit is furtherbased upon said hydraulic line pressure.
 5. The method of claim 2,wherein said commanding activation of said active cooling circuitcomprises: selecting a flow management valve to an active electricmachine cooling enabled position; and selecting a pressure controlsolenoid position to an open position to allow flow to said activecooling circuit.
 6. The method of claim 1, further comprising:monitoring a temperature of a second electric machine; determining acooling flow requirement for a cooling circuit of said second electricmachine based upon said temperature of said second electric machine;comparing said cooling flow requirement for the cooling circuit of saidsecond electric machine to a threshold cooling flow; and requestingactive electric machine cooling of said second electric machine basedupon said comparing.
 7. The method of claim 6, further comprising:monitoring flow requirements of other functions served by said hydrauliccontrol system; and commanding activation of at least one active coolingcircuit of said electric machines based upon said requesting activeelectric motor cooling of said electric machines, said temperatures ofsaid electric machines, and said flow requirements of other functions.8. The method of claim 7, further comprising: monitoring a hydraulicline pressure of said hydraulic control system; and wherein saidcommanding activation of at least one active cooling circuit of saidelectric machines is further based upon said hydraulic line pressure. 9.The method of claim 7, further comprising: monitoring a hydraulic linepressure of said hydraulic control system; and modulating operation offunctions served by said hydraulic control system based upon saidmonitoring said hydraulic line pressure.
 10. The method of claim 7,further comprising: monitoring a hydraulic line pressure of saidhydraulic control system; and modulating operation of an auxiliaryhydraulic pump based upon said monitoring said hydraulic line pressure.11. The method of claim 1, further comprising: monitoring a baseelectric machine cooling flow; and wherein said determining said coolingflow requirement for said cooling circuit is further based upon saidbase electric machine cooling flow.
 12. The method of claim 1, furthercomprising: monitoring a hydraulic line pressure of said hydrauliccontrol system; and modulating operation of an auxiliary hydraulic pumpbased upon said monitoring said hydraulic line pressure.
 13. Method forcontrolling a powertrain comprising an electro-mechanical transmissionmechanically-operatively coupled to an internal combustion engine andfirst and second electric machines adapted to selectively transmitmechanical power to an output member, said method comprising: monitoringtemperatures of said first and second electric machines; determining abase electric machine cooling flow for a base electric machine coolingcircuit providing a hydraulic flow to said first and second electricmachines; and commanding active cooling of said first and secondelectric machines based upon base electric machine cooling flow, saidmonitored temperatures, a power loss of a hydraulic pump, andoperational state of said powertrain.
 14. The method of claim 13,wherein said commanding active cooling of said first and second electricmachines comprises: determining a cooling flow requirement to said firstand second electric machines based upon said monitored temperatures;requesting active cooling of said first and second electric machinesbased upon said monitored temperatures and said base electric machinecooling flow; determining prioritization among functions requiringhydraulic flow based upon said power loss of said hydraulic pump andsaid operational state of said powertrain; and commanding active coolingof said first and second electric machines when said prioritizationenables hydraulic flow to said first and second electric machines. 15.Apparatus for controlling a powertrain comprising an electro-mechanicaltransmission mechanically-operatively coupled to an internal combustionengine and first and second electric machines adapted to selectivelytransmit mechanical power to an output member, said apparatuscomprising: said first and second electric machines; a first electricmachine cooling circuit directing a cooling hydraulic flow to said firstelectric machine; a second electric machine cooling circuit directing acooling hydraulic flow to said second electric machine; a hydrauliccontrol system receiving a hydraulic flow and selectively channelingsaid hydraulic flow to said first and second electric machine coolingcircuits; and an active electric machine cooling control systemmonitoring temperatures of said first and second electric machines,monitoring operation of said hydraulic control system, and selectivelycontrolling said hydraulic control system.
 16. The apparatus of claim15, wherein said active electric machine cooling control systemcomprises: a first hydraulic powertrain cooling module inputting saidtemperatures of said first and second electric machines and outputtingcooling flow requirements of said first and second electric machines; asecond hydraulic powertrain cooling module inputting said cooling flowrequirements of said first and second electric machines and outputtingan active electric machine cooling request; and a hydraulic controlcommand module inputting said active electric machine cooling request,monitoring operation of said hydraulic control system, and selectivelycontrolling said hydraulic control system.
 17. The apparatus of claim15, wherein said hydraulic control system comprises: a flow managementvalve selectively enabling said cooling hydraulic flows to said firstand second electric machines.
 18. The apparatus of claim 17, whereinsaid hydraulic control system further comprises: a pressure controlsolenoid selectively directing said hydraulic flow to said firstelectric machine cooling circuit; and a pressure control solenoidselectively directing said hydraulic flow to said second electricmachine cooling circuit.